Color Blindness Test: What Is It and How Is It Done?
This guide covers the cone cells in the retina, the most common red-green color vision deficiency, complete color blindness (achromatopsia), color vision tests and acquired color loss.
Color blindness means that one of the color-sensing cone cells in the retina is missing or works differently. The most common type is inherited red-green color vision deficiency. It affects about 8% of men of European descent and about 0.4% of women. Complete color blindness (achromatopsia), where no color can be told apart, is very rare. A color blindness test at an eye exam makes the diagnosis, for example with color plates that hide numbers among dots. However, color loss that appears later, especially in one eye, can be a sign of disease.
How do we see colors?
The retina has two types of light-sensitive cells. Rods let us see in dim light. Cones handle daytime vision and sense color. There are three types of cones, and they respond mostly to blue, green and red wavelengths. The brain compares the signals from these three cone types, so it can tell thousands of shades apart.
If one cone type is missing or works differently, some colors look alike. Therefore "color blindness" usually does not mean seeing no color at all. Most of the time, it means confusing certain colors.
"If one of the red, green or blue cones does not work, we cannot tell those shades apart. If none of them works, the result is complete color blindness. If you cannot read the numbers on the test plates, see an eye doctor."
— Prof. Dr. Fırat Helvacıoğlu, from his video
Color blindness test
Prof. Dr. Fırat Helvacıoğlu explains color vision and the color blindness test.
How do we see colors, and what changes in color blindness?
The three types of cone cells in the retina respond to light of different wavelengths. If one of them is missing or works differently, some colors get confused.
- Cone cellsThere are three cone types, most sensitive to blue, green and red light. The brain perceives color by comparing their signals.
- Color plateColor vision tests use numbers hidden among dots. This image is only an example, not a screening test.
- Red-green deficiencyIn the most common type, red and green shades look similar.
Types of color blindness
| Type | What happens? | Frequency |
|---|---|---|
| Red-green color vision deficiency (commonly called daltonism) | Red, green, brown and orange shades are confused. | Most common type; about 8% of men of European descent, 0.4% of women |
| Blue-yellow color vision deficiency | Blue may be confused with green, and yellow with pink. | Rare |
| Complete color blindness (achromatopsia) | Colors cannot be told apart. Visual acuity is usually low, and light sensitivity and eye tremor often come with it. | Very rare |
The genes for red-green deficiency sit on the X chromosome, so it is much more common in men. Women are often carriers. Inherited color vision deficiencies do not progress, and they do not affect other visual functions. Achromatopsia, however, is a separate and more severe condition.
How is a color blindness test done?
- Color plates: You are asked to read numbers hidden among dots of different colors. This is the most common screening test.
- Color arrangement tests: You arrange colored caps in order of shade. This shows the type and degree of the deficiency.
- Additional tests: If needed, the doctor checks the retina and optic nerve with OCT. If achromatopsia is suspected, electrophysiological tests are done.
Online and phone tests can give an idea. However, screen settings and lighting can change the result, so a definitive assessment is made at the exam. The color blindness test is part of a general eye exam.
Acquired color loss
Sometimes a person who saw colors normally before notices them fading, especially in one eye. This is not a congenital condition, and it needs investigation. Optic nerve inflammation, glaucoma, macular diseases and some medicines can affect color vision. Examples are long-term hydroxychloroquine or certain tuberculosis drugs.
See a doctor without waiting
- Colors, especially red, look faded in one eye
- Pain with eye movement or reduced vision along with the color loss
- A change in color vision while you take long-term medication
Daily life and career choice
Most people with a congenital color vision deficiency go about daily life comfortably. Often they only notice the condition during a test. However, some jobs set special color vision requirements because telling colors apart is critical. Examples are piloting, some military and security duties, and electrical wiring. Therefore it helps to test color vision before choosing a career, especially in childhood and adolescence. Today there is no definitive treatment for congenital color blindness. Some tinted filter lenses can raise contrast for certain tasks, but they do not restore normal color vision.
Frequently asked questions
Tests such as color plates reveal it. If you struggle to read the numbers hidden among the dots, an eye exam is recommended.
In everyday speech, daltonism usually means the most common type, red-green color vision deficiency. Complete color blindness (achromatopsia), where no color is seen, is very rare and a separate condition.
The genes for the most common red-green deficiency are on the X chromosome. Men have only one X chromosome, so the condition appears much more often in them.
Today there is no definitive treatment for congenital color vision deficiency. For color loss that appears later, however, treating the underlying cause is important.
Many people with a color vision deficiency can get a driver’s license. However, conditions differ by profession and license type, so check the relevant medical report criteria.
Related pages
References
- Birch J. Worldwide prevalence of red-green color deficiency. J Opt Soc Am A Opt Image Sci Vis. 2012;29(3):313-320. doi:10.1364/JOSAA.29.000313
- Aboshiha J, Dubis AM, Carroll J, Hardcastle AJ, Michaelides M. The cone dysfunction syndromes. Br J Ophthalmol. 2016;100(1):115-121. doi:10.1136/bjophthalmol-2014-306505
This article is for patient information only; it does not replace an examination or medical evaluation. The treatment that suits you is decided after an eye exam and measurements. Publication date: September 25, 2026.
Contact Prof. Dr. Fırat Helvacıoğlu with your questions
Prof. Dr. Fırat Helvacıoğlu · Veni Vidi Eye Clinic, Bağdat Cad. No: 257, Caddebostan – Kadıköy / Istanbul